The present invention relates generally to catheter probes, which direct optical energy for diagnostic or therapeutic purposes. More specifically, the invention relates to catheter probes using optical coherence tomography having a fixed or stationary optical imaging fiber.
Generally speaking, Optical Coherence Tomography (“OCT”) is a technology that allows for non-invasive, cross-sectional optical imaging of biological media with high spatial resolution and high sensitivity OCT is an extension of low-coherence or white-light interferometry, in which a low temporal coherence light source is utilized to obtain precise localization of reflections internal to a probed structure along an optic axis. This technique is extended to enable scanning of the probe beam in the direction perpendicular to the optic axis, building up a two-dimensional reflectivity data set, used to create a cross-sectional gray-scale or false-color image of internal tissue backscatter.
OCT uses a superluminescent diode source or a tunable laser source emitting a 1300 nm wavelength, with a 50-250 nm bandwidth (distribution of wave length) to make in situ tomographic images with axial resolution of 2-20 μm and tissue penetration of 2-3 mm. OCT has the potential to image tissues at the level of a single cell. In fact, the inventors have recently utilized broader bandwidth optical sources, so that axial resolution is improved to 4 μm or less. With such resolution, OCT can be applied to visualize intimal caps, their thickness, details of their structure including fissures, the size and extent of the underlying lipid pool, and the presence of inflammatory cells. Moreover, near infrared light sources used in OCT instrumentation can penetrate into heavily calcified tissue regions characteristic of advanced coronary artery disease. With cellular resolution, application of OCT may be used to identify other details of the vulnerable plaque such as infiltration of monocytes and macrophages. In short, application of OCT can provide detailed images of a pathologic specimen without cutting or disturbing the tissue.
OCT can identify the pathological features that have been associated with vulnerable plaques. The distal end of the optical fiber is interfaced with a catheter for interrogation of the coronary artery during a heart catheterization procedure. The reflected light from the plaque is recombined with the signal from the reference mirror forming interference fringes (measured by a photovoltaic detector) allowing precise depth-resolved imaging of the plaque on a micron scale.
An OCT catheter to image coronary plaques have been constructed. (Jang I K, Bouma B E, Hang O H, et al. Visualization of coronary atherosclerotic plaques in patients using optical coherence tomography: comparison with intravascular ultrasound. JACC 2002; 39: 604-609, incorporated by reference herein). The prototype catheter consists of a single light source and is able to image over a 360-degree arc of a coronary arterial lumen by rotating a shaft that spins the optical fiber. Because the rotating shaft is housed outside of the body, the spinning rod in the catheter must rotate with uniform angular velocity so that the light can be focused for equal intervals of time on each angular segment of the coronary artery. Mechanical drag in the rotating shaft can produce significant distortion and artifacts in recorded OCT images of the coronary artery. Unfortunately, because the catheter will always be forced to make several bends between the entry point in the femoral artery to the coronary artery (e.g., the 180 degree turn around the aortic arch), uneven mechanical drag will result in OCT image artifacts As the application of OCT is shifted from imaging gross anatomical structures of the coronary artery to its capability to image at the level of a single cell, non-uniform rotation of the single fiber OCT prototype will become an increasingly problematic source of distortion and image artifact.
Consequently, endoscope type single channel OCT systems suffer from non-constant rotating speed that forms irregular images of a vessel target. See U.S. Pat. No. 6,134,003, which is hereby incorporated by reference. The use of rotating single mode fibers is prone to artifact production in the OCT image. The catheter will always be forced to make several bends from its entry in the femoral artery, to the 180-degree turn around the aortic arch, to its final destination in the coronary artery. All these bends will cause uneven friction on the rotary shaft, and uneven time distribution of the light on the entire 360-degree arch of the coronary artery. As the application of OCT is shifted from gross anatomical structures of the coronary artery to its capability to image at the level of a single cell, then non-uniform rotation of the single fiber OCT will become even a greater source of image artifact.
The present invention overcomes many of the problems associated with transducing motion in remote locations such as the distal end of an optical or ultrasonic imaging catheter inside the body, such as non-uniform rotational distortion (NURD) associated with direct mechanical actuation along a shaft, biocompatibility hazards associated with delivering substantial electrical currents or voltages to actuate motors or magnets, biocompatibility hazards and fluid dynamic limitations associated with using pressurized liquid or gas to actuate a turbine. The advantage of the present invention is that it delivers light to the internal volume of the thermal gradient, which is more efficient and less constrained.